As is conventional in the prior art, optical systems traditionally operate in either mid-wave infrared regions (MWIR) or long-wave infrared regions (LWIR) but not typically both at the same time. One of the primary reasons for not processing both mid-wave infrared and long-wave infrared wavelengths together is that it is extremely difficult to capture and simultaneously focus both mid-wave infrared and long-wave infrared wavelengths, using a single imaging system comprising a series of transparent materials or lens, on an imaging or focal plane. This imaging problem, of both mid-wave infrared and long-wave infrared wavelengths, is compounded if the optical lens system is intended to operate over a wide range of operating temperatures. Such a wide range of operating temperatures is normally present when the optical lens system is intended to be utilized in an aircraft, for example, where the optical lens systems is normally subject to extremely cold operating temperatures, e.g., when the aircraft is flying at high altitudes, and may also be subject to extremely hot operating temperatures, e.g., when, for example, the aircraft is parked on an airfield, between flights, on a hot summer day.
As a result of the above noted problems, the most efficient way to solve certain optical sensing and detection problems is to operate the optical lens system either exclusively in the mid-wave or exclusively in the long-wave infrared regions. Additionally, as briefly alluded to above, traditional optical lens systems typically do not remain in focus over a wide range of operating temperatures unless such optical systems include extremely expensive and complex mechanical arrangements which are designed to compensate for the temperature fluctuations and mechanically alter the orientation of the lens as the temperature of the optical lens system varies.
Finally, the entrance pupil location, for traditional mid-wave infrared and long-wave infrared optical systems, has normally been located at a location that is behind the optical lens system. For application of an optical lens system in an aircraft, for example, it is often difficult to be able to locate the imaging or optical lens system so that the entrance pupil can be located behind at least the first lens of the optical lens system.